Messages in this thread | | | Date | Tue, 22 Jul 1997 19:01:44 +0200 (MET DST) | From | Ingo Molnar <> | Subject | Re: About ioremap() and L2-Cache |
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On Tue, 22 Jul 1997, Para Group wrote:
> Hi, every one > I read the ioremap source of Linux-2.1.x and find the kernel doesn't care > about the Pentium new bit setting PWT ( page cache write through ) and PCD > ( page cache disable ), only PCD is defined but never used in the kernel source.
check out include/asm-i386/io.h:ioremap_nocache(), that function was added around ~2.1.30. It sets the PCD flag. It's unclear (to me at least) what effect this has on PCI space memory caching. (i thought that area was uncacheable always, but there was at least one memory-mapped [custom] PCI device where this function prevented strange crashes ... so it seems to have some effect).
about the PWT bit. if it's needed, __ioremap(flags) can be called with any caching flag. (which will be written into the page table entry). Is there any RL use for the PWT bit?
-- mingo
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